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If you are lucky enough to own a garden, it may have happened to you to see it distorted by the earth mounds characteristic of these charming beasts that are the moles. Perhaps you have tried to get rid of it by one of the many means marketed: poisoned seeds, smoke cartridges, traps to place in galleries, etc. ?
All these processes have at least three common features: they are expensive, laborious to implement and quite inefficient. For a few months now, a new device has appeared under the more or less common name of "electronic molehunter". For what we know, this system has at least one common point with its predecessors: it is sold relatively expensive. What is certain is that it is easy to implement; In terms of efficiency, we leave it to you to judge, because we do not want to feed a sterile polemic here.
It is, indeed, a montage of this type that we propose to realize now, with however, a significant difference compared to its commercial counterparts since our realization, even with good will, should hardly come back to you very expensive.

The scheme
All commercial devices generate sounds, of average frequency, for about one second every ten or fifteen seconds. Since they must be driven about 20 cm underground, the sound vibrations produced are supposed to terrorize the moles and cause them to leak in a variable radius depending on the effectiveness of the device and the advertising document of the manufacturer!
Just listen to one of these devices to recognize the unpleasant noise produced by any commercial electronic buzzer.
From there to design our scheme there is only one step since a vulgar 555, chosen if possible in MOS technology to minimize the consumption, is mounted in astable oscillator of cyclic ratio of the order of 10/1 approximately.
Given the polarity of the output signal of such a circuit, a transistor performs the necessary reversal and directly controls one of the buzzers that we mentioned above. The latter is thus powered for about one second and remains silent for the next ten seconds. The exact values ​​of these times are of no great importance and depend essentially on the capacitor C1. Since it is a chemical, considerable variations are to be expected from one assembly to another.

The elongated printed circuit enables it to be housed in a commercially available PVC or PVC tube, which can also accommodate four 1.5 V cylindrical cells suitable for supplying the assembly several months in succession, A voltage of 6 V.
A realization as tight as possible is to be envisaged with just one screwed end to allow the change of the piles. For this purpose, the PVC drain fittings are wonderful. They are easy to assemble and have threaded plugs with seals (initially intended to make "looks" in the exhaust pipes).
In terms of efficiency and area of ​​action, your setup is at least as effective as its commercial counterparts, but it is much cheaper!

■ Nomenclature of components
Resistors 1 / 2or 1 / 4W5%
R1: 470 kO R2: 150 kO R3: 12k0
C1: 10 mF 15 V chemical radial C2: 100 mF 15 V chemical radial
ICi: 555, MOS version if possible T1: BC 557, BC 558, BC 559
Electronic buzzer 6 V

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